Magnetic bubble domain generator and annihilator

ABSTRACT

Magnetic bubble domain generator and annihilator for use in a magnetic bubble domain memory device of the major-minor bubble propagation path type. The magnetic bubble domain generator and annihilator structure employs a thin metallic loop which is disposed adjacent to a bubble propagation path and is alternatively operable in both a bubble generation and bubble annihilation mode. A DC bias field is provided to the magnetic bubble domain memory circuit device and exists within the metallic loop of the bubble generator and annihilator structure. Upon applying a current pulse to the thin metallic loop from a pulse generator, the bubble generator and annihilator structure is caused to operate in one of the two possible modes. When the current pulse reduces the DC bias field below a predetermined value, the metallic loop operates as a generator to generate a magnetic bubble. Conversely, when the current pulse raises the DC bias field within the metallic loop above a predetermined value, a magnetic bubble within the loop is annihilated.

This is a division of application Ser. No. 499,823, files Aug. 23, 1974now U.S. Pat. No. 4,040,019

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to magnetic cylindrical (bubble) memory devicesand more particularly to a more closely packed arrangement of suchdevices, means of fabrication of such arrangement and means formanipulating and otherwise handling of such an arrangement.

2. Description of Prior Art

The term "bubble" sometimes referred to as a "single wall domain,"refers to a magnetic region encompassed by a single domain wall whichcloses on itself in the plane of the material in which the domain ismoved. Inasmuch as a domain is self-contained in the plane of thematerial and does not intersect the edge of the material, it is free tomove in that plane in response to consecutively offset fields. A domainof this type is described in the Bell System Technical Journal (BSTJ)Vol. XLVI, No. 8, (1967) at page 1901.

The fields which move single wall domains are typically generated bypulses in series-connected conductor loop sets. The sets are pulsed insequence to generate repetitive field patterns for movinginformation-representative domain patterns. Individual conductors can bepulsed also in a programmed manner to effect data processing functionsbetween selected domains. A conductor arrangement of this type requiresa number of external connections which are, preferably, kept to aminimum.

An alternate implementation for generating the field patterns for movingdomains employs magnetically soft overlay patterns of Permalloy materialwhich generate magnetic poles in response to fields in the plane of thematerial. The in-plane field is reoriented causing movement of the polesand, consequently, movement of the domains which are attracted by them.A pattern employing the popular T and bar shaped Permalloy overlayelements is described in U.S. Pat. No. 3,613,058, among others. Chevronshaped elements are described in U.S. Pat. No. 3,729,726 among others.

The more popular of the two systems just described is the T and barshaped arrangement, which allows bubbles to be propagated in eitherdirection therealong in accordance with inplane field direction.Although generally acceptable, some difficulty with the T and bar shapedPermalloy organizations have been observed. The major difficultyobserved is caused by the gaps or the spacing between the soft magneticelements. The narrower the gaps the better the circuit operates. But,the quality control problem achieving uniform and narrow gaps isextremely serious. A second problem is caused by the corners of suchPermalloy circuits. To conserve space, the loops are elongated andinclude sharp double back curves or corners. Although such arrangementswork satisfactorily in many relatively low frequency applications, theyhave proven unsatisfactory at higher frequencies and higher bitdensities.

An alternate means to the Permalloy propagation patterns of defining apath along which bubbles are sustained and can be moved has beendeveloped and is known as the localized ion implantation technique. Suchimplantation through a patterned photoresist mask may be used to alterthe magnetic anisotropy of magnetic garnets and to thereby produce railswhich guide bubbles in garnet epitaxial films.

The patterns established for magnetic memory organizations using the ionimplanted garnet technique have followed the well known pattern of thePermalloy arrangements. One popular family for Permalloy circuits is themajor-minor loop pattern shown, for example, in U.S. Pat. Nos.3,613,056; 3,618,054 and 3,729,726 among others. In such anorganization, read and write connections are made to the major loop anddata bubbles are exchanged from the minor loops and the major loop attransfer gates, where the loops come into close proximity with oneanother. The advantage of such an organization is that the magneticrotating fields do not have to be reversed since all data is confinedwithin continuous loops that provide a circulating data path. An analogymay be made to a magnetic rotating drum that carries the data again andagain past the same point for data reading and writing.

Hybrid arrangements of the major-minor loops configuration, such asshown in U.S. Pat. No. 3,613,058, have continuous minor loops, but asingle path to the read and write circuitry. Such organization orarrangement lends simplicity and short access to the stored data, butrequires in-plane magnetic field rotation reversals, and has not hadwide spread acceptance.

Ion implanted garnet circuits following the organizations of thePermalloy circuits have heretofore taken up large amounts of area on achip. That is, the major and minor loops in the arrangement justdescribed have heretofore been formed by stringing the non-implantedcircles one after another until the string closes on itself. When it isremembered that the domain or bubble size is only a fraction of thenon-implanted circular areas forming the path, it may be seen that evenone loop takes up considerable space. Further, using conventionalphotoresist masking techniques, the masked circular areas tend to beill-defined at their cusps, that is, at the junction points between thecircular areas, as contrasted to the regions exposed to ion implantationand comprising the remainder of the surface structure of the magneticgarnet layer. Each loop of non-implanted circles is elongated andalthough both inside and outside surfaces of the loops are theoreticallysuitable for travel of the domains, only travel on the outside has beensatisfactory. This is because only at the outside is loop-to-looptransfer permitted without external wiring. Moreover, outside travel isused to prevent unwanted across-the-loop transfer, since to conservespace the distance across the loop is kept quite short.

Finally, it has been thought heretofore that loop-to-loop transfer, thatis, between the minor loops and the major loop, had to take place wherethe loops were closest to each other. This is true of the transfer gateof a T-bar Permalloy circuit. However, one shortcoming of an ionimplanted garnet circuit major-minor loop arrangement has been that ifthe circular non-implanted area of a minor loop is directly abreast ofone of the circular areas of the major loop, then at the instant whenthe propagating field at the edge of the minor loop is suitable torelease the bubble, the field at the major loop is not of the correctphase to receive the bubble. It has been necessary, therefore to retainthe bubble at the end of the minor loop for one-half of the clock perioduntil the phase of the field at the major loop is correct to accept thebubble, a very unhandy operating phenomenon.

Therefore, it is one feature of the present invention to provide animproved embodiment of an ion-implanted garnet, major-minor looparrangement in which the non-implanted areas are formed in rows.

Another feature of the present invention is to provide an improvedembodiment of an ion-implanted magnetic bubble memory device employingnon-implanted areas comprising major and minor rows in an otherwiseion-implanted magnetic garnet that provide transfer of bubbles from loopto loop wherein the releasing loop and receiving row are offset topermit bubble release and acceptance operating at the same phase of thepropagating field.

Yet another feature of the present invention is to provide an improvedmethod of masking an organization to provide contiguous, circularnon-implanted areas in an otherwise ion-implanted garnet areas so thatthe cusps formed between in the circular non-implanted areas are sharplydefined, thereby providing trouble-free high speed data propagation.

Still another feature of the present invention is to provide improvedmeans of bubble generation, replication and annihilation in conjunctionwith an ion-implanted magnetic bubble memory device having a major-minorloop arrangement in which the non-implanted areas are formed in rows.

SUMMARY OF THE INVENTION

A prefered embodiment of the present invention comprises a bubbledomain, major-minor organization formed with respect to an ion-implantedgarnet film. The regions which are masked during ion implantation aresubstantially circular and are contiguously grouped in rows to providenon-implanted regions adjacent to the ion-implanted regions comprisingthe remainder of the garnet film surface. The edges of the ion-implantedregions adjacent to the non-implanted regions form rails to which thebubble data domains adhere and along which they are propagated. Theminor rows of non-implanted regions are preferably positioned so thatthe end regions thereof are aligned opposite cusps in the major row. Inthis position, the rotating in-plane magnetic field properly aligns thebubbles for release and access with appropriate clock pulsing meanswithout having to hold a bubble for a 180° phase rotation of the field.

A conducting loop in contact with a non-implanted region may be used forbubble generation and annihilation with appropriate current pulsing.Also, a similar loop may be used as a replicator in conjunction with anon-implanted region and an expansion detector comprising Permalloyelements.

Finally, the non-implanted regions are made to have sharply definedcusps and better defined edges when the masks used in their manufactureare a thin metal alloy, rather than photoresist. Regions made in thismanner assure reliable high speed application.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features, advantages andobjects of the invention, as well as others which will become apparent,are attained and can be understood in detail, more particulardescription of the invention briefly summarized above may be had byreference to the embodiments thereof which are illustrated in theappended drawings, which drawings form a part of this specification. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of the invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

In the drawings:

FIG. 1 is a cross-sectional view of a masked circular region and an ionimplanted region adjacent thereto in accordance with the presentinvention.

FIG. 2 is a diagram illustrating a simplified model of bubblepropagation with respect to non-implanted regions.

FIG. 3 is a diagrammatic representation of a reverse domain in theimplanted layer at the edges of non-implanted region.

FIG. 4 is a diagram illustrating a model of bubble propagation withrespect to non-implanted regions using the reverse domain theory.

FIG. 5 is a plan view of a major-minor bubble memory organization inaccordance with a preferred embodiment of the present invention usingion implanted garnet film.

FIG. 6 is a simplified diagram of a prior art memory loop using ionimplanted garnet film with non-implanted regions arranged in a loop.

FIG. 7 is a simplified diagram of a row of non-implanted regions asemployed in the present invention.

FIG. 8 is a partial diagram of a transfer of reverse domains from minorrows to a major row when the end regions of the minor rows are abreastregions of the major row.

FIG. 9 is a partial diagram of the transfer action illustrated in FIG. 8with the in-plane field located 180° from the position shown in FIG. 8.

FIG. 10 is a diagram of the transfer action of reverse domains fromminorrows to a major row when the end regions of the minor rows areabreast cusps between two regions of the major row.

FIG. 11 is a diagram of a generator and annihilator in accordance withthe present invention.

FIG. 12 is a diagram of a section of a Permalloy chevron propagationpath leading to a Permalloy expansion detector and a replicator (notshown) in accordance with the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Localized ion implantation through patterned photoresist masks has beenused to produce rails which guide domains or bubbles in magnetic garnetepitaxial films secured to non-magnetic garnet substrates. Implantationexpands the lattice structure so that the implanted regions are inlateral compression. In magnetic garnets with negative magnetostriction,the shallow regions have stress-induced easy axes parallel to the filmsurface. Bubbles adhere to the edges of the implanted regions because ofmagnetostatic and magnetoelastic effects. The in-plane magnetization inthe implanted regions can be rotated by an in-plane applied field, aswith the Permalloy circuits in the prior art. Bubbles in the underlyinggarnet follow the moving poles at the edges of the implanted regions.

Now referring to FIG. 1, an edge view of an implanted region and anon-implanted region adjacent thereto in accordance with the abovedescription is illustrated. The non-magnetic garnet substrate 10 isoverlayed with a magnetic garnet film 12 over which photoresist material14 is used to define the circular regions to be masked while theremainder of the magnetic garnet film 12 is subjected to ionimplantation. One successful masking material has been a Waycoat resistwhich is 12,000 A thick. Implanting is done, for example, with 2 × 10¹⁶protons/cm² of 100 keV energy. Thus, the area 16 outside of the circularphotoresist element 14 is implanted. Bubbles are propagated in the ionimplanted circuit owing to the presence of magnetic poles which arecaused by the discontinuity in the transverse component of themagnetization junction between the implanted and unimplanted regions.The in-plane magnetization in the implanted region can be rotated by anin-plane applied field, as with the prior art Permalloy circuits.Bubbles 18 in the underlying garnets follow the moving poles at theedges of the implanted regions. Thus, the non-implanted regions definedin the implanted layer take the place of the superimposed Permalloypattern wherein the edges of the ion-implanted regions adjacent to thenon-implanted regions form rails along which the bubbles may bepropagated. Propagation of 5 micrometer diameter bubbles at a rate of100 kHz has been achieved in a magnetic garnet film of the followingcomposition: (YGdTm)₃ (FeGa)₅ 0₁₂.

To understand how a bubble propagates along a row of contiguous circularregions, reference is made to FIG. 2, wherein is illustrated anexamination of a few possible cases for the magnetic pole distributionat the boundaries. The simplest case is to assume that the in-planedrive field completely saturates the magnetization in the implantedlayer. Assume that bubble 18 is attracted to the positive head 20 of thevector representing the drive field. The model illustrated starts withbubble 18 at the left end of the row of four circles 22, 24, 26 and 28.Rotating drive field 20 is successively positioned in the four relateddiagrams to the right, straight down, to the left, and straight up,respectively. For the first three clock phases, the bubble follows thepositive pole distribution properly. However, at the fourth position, inthe cusp between circles, it is subjected to a negative poledistribution, which will repel it away from the propagating track orrail. Hence, the pole distribution as shown is not completely adequateto explain propagation of magnetic bubbles.

Now referring to FIG. 3, a diagrammatic representation of reversedomains in the implanted layer at the edges of an implanted region isillustrated. This reverse domain theory has been postulated to explainthe fact that the bubble propagating around the circle is actually of apolarity opposite to that expected from the uniformly magnetizedimplanted layer of FIG. 3. Now referring to FIG. 4, a diagramillustrating bubble propagation with respect to rows of non-implantedregions using the reverse domain theory is illustrated. It is postulatedthat during steps 1 and 2, the reverse domain follows in phase with therotation of the in-plane drive field. In steps 3, 4 and 5, however, theposition and extent of the reverse domain is different from what itwould be with an isolated circle. The most critical point is shown instep 4 where the closure domain contracts far into the cusp between thecircles. This allows positive poles to be induced on the sides of thecusps and causes the bubble to be held tightly, rather than repelled.There is still a slight repulsive interaction of the bubble due to thereverse domain as the bubble traverses the cusp. However, the modelillustrated appears to be adequate to explain the results of themagnetostatic, magnetoelastic and exchange interactions of a bubbletraversing the track or rail formed by the edges of the ion-implantedregions adjacent to a row of contiguous non-implanted garnet regions.

Now referring to FIG. 5, a plan view is shown of a major-minor mobilememory organization in accordance with a preferred embodiment of thepresent invention using ion implanted magnetic garnet film 12, asdescribed above. The arrangement shows a layer of magnetic garnetepitaxial film 12 in which single wall domains are supported and causedto be propagated with respect to rows of contiguous non-implantedregions, with the remainder of the magnetic garnet epitaxial film 12being ion-implanted. A bias field supplied by source 50 maintains singlewall domains in the material at nominal operating size, as is wellknown. Rotating field source 52 causes movement of the domains to occur,normally couterclockwise. The rotating field source 52 is under thecontrol of a control circuit 54 for activation and synchronization.

The bias sources, control circuit and other auxiliary circuits (such aspulsing circuits for application to the transfer gates, counter circuitsfor tracking the bubbles along their propagating rows, etc.) are wellknown. Although not specifically illustrated in each case, such circuitsmay be used with the illustrated embodiment.

The organization illustrated in FIG. 5 includes a major row 56 ofnon-implanted regions substantially circular in configuration andcontiguously grouped. Similarly, a plurality of minor rows, which may beconsidered identical to one another, are similarly comprised ofnon-implanted regions that are circular in nature and contiguouslygrouped in rows. The minor rows are positioned in either side of majorrow 56 and are preferably at right angles to the major row.

Before describing the operation of the organization illustrated in FIG.5, attention should now be given to FIGS. 6 and 7, which are simplifieddrawings. A prior art structure is illustrated in FIG. 6 and the basicrow structure of the FIG. 5 embodiment is shown in FIG. 7. In the FIG. 6embodiment, circular non-implanted regions 60 are arranged in a loop onan otherwise ion-implanted magnetic garnet film, similar to themajor-minor loop arrangements employing Permalloy circuits, as disclosedin the prior art. Bubbles 62 travel along the outside edge of the loopformed by such regions from cusp to circular edge, to cusp, in themanner described for FIG. 4. At the illustrated time, it may be seenthat the bubbles are in the cusps on the bottom while on the outerperipheral edges of the circular regions at the top. As illustrated, thein-plane field is in an upward direction.

In the embodiment of the row shown in FIG. 7, a single row ofnon-implanted regions permits bubbles 62 to travel in loop fashionaround the row and along the edge or rail defined by the edges of theion implanted regions adjacent to the row of non-implanted regions. Ithas been discovered, that even at high speeds, bubbles do not separatefrom the edge of the regions at the end of the rows, as sometimes occurswith the T-bar Permalloy circuits. Further, it has been discovered thatthe rows act in every other regard equal in operation to the looparrangement defined in FIG. 6, when arranged in a minor-major looporganization, such as illustrated in FIG. 5. The compactness of thedata, as well as a reduction in the number of non-implanted regions, isreadily apparent. Notice that FIG. 7-type rows are used for both themajor track and the minor tracks.

To obtain optimum access time in the transfer gate between the major andminor rows, it has been discovered that the end region of each minor rowshould be positioned opposite a cusp in the major row. When the endregion of a minor row is positioned abreast a region in the major row,the action of transfer is as illustrated in FIGS. 8 and 9. In theabreast arrangement, transfer from the minor rows to the major row iseffected by both blocking the magnetic poles of the circles at the endsof the minor rows and lowering of the bias field in the transfer region,denoted by "d."To transfer from the major row into the minor rows, themagnetic poles on the sides of the major row adjacent to the minor rowsare blocked. Blocking is effected by a suitably shaped current carryingconductor. For this type of transfer, the number of clock cycles topropagate a bubble completely around the major row must be an integralmultiple minus one of the number of clock cycles necessary to propagatea bubble around a minor row. This condition may be achieved by slightlyincreasing the radius of the circles on one side of the major row inorder to reduce the total number of circles in the major row.

In FIG. 8, the reverse domain at the end region of the minor row ispositioned and ready for release to the major row; however, the regionin the major row is of the opposite polarity necessary for accepting thetransfer. That is, the field at the edge of the major row is not of thecorrect phase to receive the bubble. It is necessary, therefore, toretain the bubble at the end of the minor row for one-half of a clockperiod until the phase of the field at the major row is correct toaccept the bubble, as illustrated in FIG. 9. Transfer is possible, butthe bubble must be held for a 180° phase rotation of the field,requiring a transfer pulse for reducing the bias field in the transferregion which must be carefully controlled with respect to duration.

Now referring to FIG. 10, a transfer arrangement is illustrated for azero-degree phase loss gate. This occurs when the end region of a minorrow is abreast the cusp between adjacent regions in the major row. Inthis arrangement, the number of bit positions in the major row is anintegral multiple of the number of bit positions in a minor row.

Notice that for the FIG. 10 gate arrangement, attractive poles exist onboth sides of the gate at the same point of the clock cycle and hencethe bubble in the gate can be transferred across in either direction bya gradient pulse. The phase of the propagating field is simultaneouslycorrect for releasing the bubble from the minor row and accepting it atthe major row, or vice versa.

The basic functions necessary for manipulating a bubble memory systemare generation, annihilation, transfer, replication and detection, allof which are used in connection with Permalloy circuits. Generation andannihilation of bubbles can be done on ion implanted circuits byconducting loops regardless of the presence or absence of Permalloyelements. Illustrated in FIG. 11 is a preferred embodiment of such agenerator and annihilator. A loop 70 of thin metal is shown adjacent theedge of end region 72 of a row of non-implanted regions as previouslydescribed. The metallic loop reduces in dimensions at the edge of region72. Preferably, the conducting loop is an alloy having, among othercharacteristics, high conductivity, such as Ti-W-Au or Cu-Al, and is astructure approximately 0.5 micrometers thick. Current means (not shown)may be applied to loop 70 for domain generation by reversing the dc biasfield within the loop 70 in the vicinity of the edge of region 72.Typically, to generate a bubble may require a current of approximately200 milliamps in a suitably shaped conducting loop.

The structure shown in FIG. 11 may be used for annihilation by raisingthe dc field within the loop 70 by application of approximately 200milliamperes of current when a bubble is within the confines of theconducting loop.

The function of replication is primarily required when an expansiondetector that destroys the data is used. Hence, a chevron propagationpath comprising Permalloy chevron elements 80 is illustrated in FIG. 12.This path may lead to an expansion detector (not shown). Replicator 81is similar to the generator and annihilator shown in FIG. 11. It ispreferably a thin loop, long enough to cover both the edge of end region82 of the row of non-implanted regions with which the replicator isused, as well as adjoining elements of the expansion detector.

As shown in FIG. 12, a domain passing through the position along theedge of region 82 confined within the loop of replicator 81 is stretchedby lowering the bias field within the loop to form a strip domain as thestretching pulse is applied and just before the domain is cut. The twochevrons that are covered by the conductor may be non-planar. After thestrip domain is cut, the domain reforms as a bubble and progresses downthe chevron path to the expansion detector while the remaining otherpart of the strip domain remains in contact with the edge of region 82.Hence, the data is not destroyed by its detection and remains in therow. This technique makes it unnecessary to return a bubble to a rowonce it has been replicated.

As started above with respect to the generator and annihilator in FIG.11, a suitable current 200 milliamps to replicator 81 is suitable fordomain replication. Further, the replicator itself may be of the samethickness and material as the generator and annihilator illustrated inFIG. 11. The expansion detector has been described with respect toPermalloy chevron elements. Permalloy T and bar elements may also beemployed and used in conjunction with replicator 81. In addition,detectors not using Permalloy elements at all may be employed withreplicator 81.

Ion implanted magnetic bubble circuits have heretofore been fabricatedthrough the use of a patterned photoresist mask. It has been difficult,however, to achieve suitable edge definition of the masked circularregions using this technique, particularly in the cusp area betweenadjacent circular regions. Therefore, it has been discovered that apatterned thin metallic layer employed as a mask achieves improveddefinition of the junctions between the non-implanted regions and theion implanted regions and also produces a stress gradient at the metaledge which penetrates into the magnetic garnet and acts as an additionaltrapping force for keeping the bubble on track. One suitable metal layerhas been a layer approximately 0.75 micron thick made of an alloy ofTi-W-Au.

While particular embodiments of the invention have been shown, it willbe understood that the invention is not limited thereto, since manymodifications may be made and will become apparent to those skilled inthe art.

What is claimed is:
 1. A magnetic memory, comprisinga magnetic garnetepitaxial layer, the upper surface portion of said magnetic layer havinga pattern formed therein defined by regions of two different types, thefirst of said regions including at least one row of contiguous regions,the second of said regions being ion-implanted regions, the edges ofwhich adjacent to said first regions form rails to which magneticdomains adhere and along which the magnetic domains may be propagated,means operably coupled to said magnetic garnet layer for controllablypositioning magnetic domains with respect to said row, said meansincluding dc field bias means, a conducting loop in contact with one ofsaid regions included in said row, and means connected to saidconducting loop for generating a current therethrough, a current pulsereducing said dc bias field below a predetermined value generating adomain and a current pulse raising said dc bias field above apredetermined value annihilating a domain within said conducting loop.2. A magnetic memory as set forth in claim 1, wherein said conductingloop is an alloy of Ti-W-Au.
 3. A magnetic memory as set forth in claim1, wherein said conducting loop is an alloy of Cu-Al.
 4. A magneticmemory as set forth in claim 1, wherein said conducting loop is a thinfilm metal structure approximately 0.5 micrometers thick.
 5. A magneticmemory as set forth in claim 1, wherein the current necessary for domaingeneration is approximately 200 milliamperes.